Nutrient digestibility of diets containing five different insect meals in gilthead sea bream (Sparus aurata) and European sea bass (Dicentrarchus labrax)

Abstract

In the recent years, insect meals have been studied as alternative feed ingredients for aquafeeds, due to their adequate nutrient composition and low ecological footprint. These studies involve nutrient digestibility measurements, as they provide valuable information on the ability of fish to utilize insect meal efficiently. In this context, the current study evaluated the nutrient digestibility in European sea bass (Dicentrarchus labrax) and gilthead sea bream (Sparus aurata) fed diets with five different insect meals. For this investigation, diets including 19.5 % of each insect meal from yellow mealworm (Tenebrio molitor – TM), black soldier fly (Hermetia illucens – HI), common housefly (Musca domestica – MD), super worm (Zophobas morio – ZM) or lesser mealworm (Alphitobius diaperinus – AD) and a control fish meal (FM) diet were tested. In European sea bass, TM and MD diets showed similar dry matter, protein, fat, energy, and organic matter ADCs among each other as well as with the FM diet (P > 0.05). However, adjusted protein ADC of TM and ZM diets (93.4 – 93.6 %) were significantly higher (P < 0.05) compared to the FM diet (91.9 %). Fat ADC was similar in all dietary groups (88.6–92.4 %; P > 0.05). The HI diet exhibited significantly lower dry matter, protein and organic matter ADCs compared to the FM diet (P < 0.05). Moreover, the AD diet presented significantly lower digestibility coefficients of dry matter, organic matter and energy than the FM diet (P < 0.05). The dietary contents of crude fiber and ash, and the inclusion of plant feedstuffs correlated negatively with various ADCs (P < 0.05). Regarding gilthead sea bream, the ADCs of dry matter, organic matter, protein, adjusted protein and energy were not affected by the different dietary treatments (P > 0.05). Fat ADC of the TM diet (73.6 %) was significantly lower compared to the other five diets (78.9–84.3 %; P < 0.05). The individual amino acid ADCs values were found to be very high in all experimental diets (90.9 – 98.0 % for European sea bass and 88.9 – 97.2 % for gilthead sea bream). In sea bass, the variation in crude protein and adjusted protein ADCs was strongly reflected on the individual amino acid ADCs. Nevertheless, the “true protein digestibility” as expressed by the sum of amino acids was not affected by the insect inclusion compared to the FM diet (P > 0.05), while a significant difference was observed between the ZM and HI diets (95.9 % and 94.1 % respectively; P < 0.05). In sea bream, the sum of amino acids and the individual amino acid ADC values did not differ among the experimental diets (P > 0.05) except for methionine (P < 0.05). Conclusively, in sea bream all diets exhibited similar overall digestibility. In sea bass, compared to the FM diet, TM and MD diets had similar or even slightly better digestibility, whilst diets HI and AD presented lower overall digestibility.